Ba3CoSb2O9 M. Li, 2 A. Zelenskiy, J. A. Quilliam, Z. L. Dun, H. D. Zhou, M. L. Plumer, and G. Quirion 2 Department of Physics and Physical Oceanography, Memorial University, St. John’s, Newfoundland, Canada, A1B 3X7 Institut Quantique and Département de Physique, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee, 37996-1200, USA (Dated: September 21, 2018)

We show that a system described by an equation of state which contains a high number of degrees of freedom (resonances) can create a considerable amount of superfluid (condensed) pions through the decay of short-lived resonances, if baryon number and entropy are large and the dense matter decouples from chemical equilibrium earlier than from thermal equilibrium. The system cools down faster in the presence of a condensate, an effect that may partially compensate the enhancement of the lifetime expected in the case of quark-gluon-plasma formation. E. Mail: ORNIK@TPRI6B.GSI.DE E. Mail:PLUEMER M@VAX.HRZ.UNI-MARBURG.DE E. Mail: DDS@T2.LANL.GOV

Properties and performance for alloy and multilayer perpendicular recording media designs utilizing a soft magnetic underlayer are compared. Among samples considered here, grain size and grain size dispersion are more highly refined for alloy media deposited at high substrate temperature, and are beginning to approach those now available in longitudinal recording. Multilayer media made at ambient temperature typically sacrifice film density and surface smoothness for interface quality. Although microstructural development and the manufacturing process for multilayer media are less mature versus alloy, multilayer media remain attractive due to their high anisotropy potential and the ease with which H-n and H-c can be controlled. For thermally stable alloy media made on a pilot production sputtering machine, a spin-stand areal density of 61 Gb/in(2) has been demonstrated at 350 Mb/s data rate with an on-track bit-error-rate reference level of 1e-6. Using the same media, a working perpendicular drive has been demonstrated at 32 Gb/in(2) and 500-800 Mb/s data rate.

Summary form only given. The micromagnetic method is utilized to explicitly verify the notion that it is not possible to saturate a soft magnetic underlayer (SUL) when the pole tip and the SUL have the same saturation magnetization. Simple magnetostatic arguments reveal that, to lowest order, saturation of the SUL would require that the moment of the pole tip (M/sub s,tip/) be twice the moment of the SUL (M/sub s,SUL/). The magnetic field under the writer pole will certainly not exceed 2/spl pi/M/sub s,tip/. In response to the write field, a demagnetization field (4/spl pi/M/sub z,tip/, z along the perpendicular direction) develops in the SUL such that the torques generated by the write field and the demagnetization fields are equal and opposite. Hence, saturation of the SUL can be safely excluded unless M/sub s,tip/spl sim/2/ M/sub s,SUL/. This fundamental observation relaxes restrictions on the choice for materials for a low SUL.

Summary form only given. The effects of medium properties on perpendicular recording is investigated through a previously developed micromagnetic model. The Finite Element Method (FEM) is used to generate head fields for a generic single-pole type writer design in the presence of a medium with a soft underlayer (SUL). Transitions are recorded with a LLG model of perpendicular recording media and read-back is performed using a micromagnetic model of a GMR spin-valve device.

A previously developed micromagnetic recording model is extended here for perpendicular recording media with a soft under layer. Write head field saturation effects are examined and shown to have a severely detrimental effect on the quality of recorded transitions. An extension of the model to account for a source of medium switching field distribution is used to study the degradation of amplitude and medium SNR with increasing linear density.

We demonstrate the feasibility of a spin-valve read head using an adjacent antiferromagnetic (AFM) layer to provide a stabilization Held, eliminating the hard bias permanent magnet layer. The head stack consists of seed/AFM/CoFe/Ru/CoFe/Cu/CoFe (and/or NiFe)/Cu/IrMn/cap where the AFM is PtMn or IrMn. The abutted junction is about 0.1 /spl mu/m wide at the free layer and no permanent magnet materials are used. Micromagnetic modeling indicates that a proper bias field is needed to have a stable head response. The bias field from the AFM layer can be modified by a nonmagnetic spacer layer between AFM and FM. The coupling field decays exponentially with the thickness of the spacer layer, consistent with a pinhole-dominated mechanism. Unshielded sensors show much higher sensitivity as,compared with a standard PM abutted junction head. Microtrack profile based on the spin-stand test shows a regular shape without apparent lumps. The electrical reader width is about 6 /spl mu/" (0.15 /spl mu/m), corresponding to a track density of 112 ktpi. Combined with a linear density of 591 kbpi the heads in this work are capable of areal density around 66 Gb/in/sup 2/.

Measurements and modeling of soft magnetic underlayer (SUL) materials for perpendicular magnetic recording application are carried out. The process dependent magnetic properties of FeCoB, CoZrNb, and FeAlN SUL materials on glass and aluminum disk substrates are studied and correlated with spin-stand noise performance. The SUL-induced do noise amplitude approaches the electronic noise floor for certain material combinations, e.g., FeCoB or CoZrNb on glass, when care is taken to relieve stress-induced perpendicular anisotropy by thermal annealing. Landau-Lifshitz-Gilbert micromagnetics, finite-element method calculations, and a micromagnetic recording model show that write field amplitude, write field gradient, and readback waveform are only slightly impacted by SUL moment in the 1-2 T range. Much more important are the head-to-SUL distance and the write head saturation moment. These results suggest that extremely high SUL moment may not be necessary, which can be leveraged to meet other key practical requirements such as corrosion resistance and manufacturability.

The recording process at 100 Gb/in(2) is examined through the use of a recently formulated micromagnetic model. The Finite Element Method is used to calculate the write head field, the Landau-Lifshitz-Gilbert equations are solved for the medium and a micromagnetic approach is used to model magnetoresistive play-back. Effects due to pole tip saturation as well as medium anisotropy distributions (orientation ratio) are emphasized. At higher currents, pole-tip saturation causes recorded tracks to be significantly wider than the physical dimensions of the writer. Narrow reader dimensions also limit the play-back signal. Both of these effects are significantly improved through the use of oriented media. Preliminary results using a novel technique to model transition noise are also reported.

Auxiliary write-head fields, either from simple analytic approximations or from finite-element computations, are used to record transitions on a Landau-Lifschitz-Gilbert model of thin-film recording media, A micromagnetic model of a magnetoresistive element is used to read back the transitions. Focus is on the impact of pole-tip saturation on the quality of the recorded track and subsequent playback. It is shown that with increasing write current, the quality of the recorded transitions degrades much more rapidly than would be expected from the analytical expressions for the write-head field. Specifically, head saturation causes the transition parameter to increase. At high write currents, poor write field gradients at the track edges result in a strong increase in transition parameter with read width percentage of the recorded track.

A micromagnetic recording model is used to examine the effects of media-grain anisotropy distributions on the quality of recorded tracks at high areal density, Write head fields derived from the Finite Element Method, which accounts for pole-tip and corner saturation, are applied to a Landau-Lifschitz-Gilbert model of thin-film Longitudinal media. The read-back signal from the recorded transitions is determined through a micromagnetic model of a GMR spin-valve device, Medium magnetization profiles, percolation, track-edge effects, and read-hack voltages are reported for 10 Gb/in(2) applications, As the anisotropy axes become more oriented along the down-track direction. both the sharpness of the transitions as well as the extent of erase bands improve dramatically, The cases of both saturated and unsaturated writer pole tips are examined. The effect of an out-of-plane component of the medium anisotropy axes is also examined. Even with a moderately wide Gaussian distribution, the effect on transition quality is minimal. Erase bands increase to some extent but the read-back signal is little affected.

A multiparticle system produced by a large number of independent sources is described by a gaussian density matrix W. All theoretical approach to Bose-Einstein Correlatios Cn in high energy physics use this form for W. One of the most salient consequences of this form is the fact that all higher order (n>2) moments of the current distribution can be expressed in terms of the first two. We test this property by comparing the data on C2(Q^2), C3(Q^2) and C4(Q^2) from pion-p and K-p reactions at 250 GeV/c with the predictions of a general quantum statistical space-time approach. Even a simplified version of such approach can account for the data. Previous attempts along these lines, which did not use the space-time approach, met with difficulties.

We calculate the π−π+ ratio for Pb + Pb at CERN/SPS energies and for Au + Au at BNL/AGS energies using a (3+1) dimensional hydrodynamical model. Without consideration of Coulomb effect an enhancement of this ratio at low mt is found compatible with that observed in these experiments. Our calculations are based on previous (3+1) dimensional hydrodynamical simulations (HYLANDER), which described many other aspects of experimental data. In this model the observed enhancement is a consequence of baryon and strangeness conservation and of chemical equilibration of the system and is caused by the decay of produced hyperons, which leads to a difference in the total number of positive and negative pions as well. Based on the same approach, we also present results for the π−π+ ratio for S + S (CERN/SPS) collisions, where we find a similar effect. The absence of the enhancement of the π−π+ ratio in the S + S data presented by the NA44 Collaboration, if confirmed, could indicate that chemical equilibration has not yet been established in this reaction.

The implications of the formation of a Bose condensate on one- and two-particle spectra are studied for ultrarelativistic nucleus-nucleus collisions in the framework of a hydrodynamic description. It is found that single-particle spectra are considerably enhanced at low momenta. The Bose-Einstein correlation function has an intercept below two. For pion pairs in the central region a two-component structure may appear in the correlation function, which is different from that found in quantum optics. The chaoticity parameter is strongly momentum dependent.

The effect of (i) the phase transition between a quark gluon plasma (QGP) and a hadron gas and (ii) the number of resonance degrees of freedom in the hadronic phase on the single inclusive distributions of 16 different types of produced hadrons for Au+Au collisions at AGS energies is studied. We have used an exact numerical solution of the relativistic hydrodynamical equations without free parameters which, because of its 3-d character, constitutes a considerable improvement over the classical Landau solution. Using two different equations of state (eos) - one containing a phase transition from QGP to the Hadronic Phase and two versions of a purely hadronic eos - we find that the first one gives an overall better description of the Au+Au experimental data at $AGS$ energies. We reproduce and analyse measured meson and proton spectra and also make predictions for anti-protons, deltas, anti-deltas and hyperons. The low m_t enhancement in pi- spectra is explained by baryon number conservation and strangeness equilibration. We also find that negative kaon data are more sensitive to the eos, as well as the K-/pi- ratio. All hyperons and deltas are sensitive to the presence of a phase transition in the forward rapidity region. Anti-protons, Omegas and heavy anti-baryons are sensitive in the whole rapidity range.

We calculate the π/π ratio for Pb + Pb at CERN/SPS energies and for Au + Au at BNL/AGS energies using a (3+1) dimensional hydrodynamical model. It turns out that it is possible to explain the low mt enhancement in the ratio observed in experiment without consideration of the Coulomb effect. Our calculations are based on previous (3+1) dimensional hydrodynamical simulations (HYLANDER), which described many other aspects of experimental data. In this model the observed enhancement is a consequence of baryon and strangeness conservation and of chemical equilibration of the system and is caused by the decay of produced hyperons, which leads to a difference in the total number of positive and negative pions as well. We analyse and predict the total multiplicity of hyperons for the different collisions. Based on the same approach, we also present results for the π/π ratio for S + S (CERN/SPS) collisions, where we find a similar effect. The absence of the enhancement of the π/π ratio in the S + S data presented by the NA44 Collaboration, E. Mail: arbex@mailer.uni-marburg.de E. Mail: ornik@warp.soultek.de E. Mail: pluemer@mailer.uni-marburg.de E. Mail: schlei@t2.lanl.gov E. Mail: weiner@mailer.uni-marburg.de

We present the first analysis of preliminary data for Pb + Pb at 160 AGeV using 3 + 1-dimensional relativistic hydrodynamics. We find excellent agreement with the rapidity spectra of negative hadrons and protons and the correlation measurements. The data indicate a large amount of stopping; 65% of the invariant energy of the collision is thermalized and 73% of the baryons are contained in the central fireball. Within our model this implies that a quark-gluon-plasma of lifetime 3.4 fm/c was formed.

We calculate the π/π ratio for Pb + Pb at CERN/SPS energies and for Au + Au at BNL/AGS energies using a (3+1) dimensional hydrodynamical model. Without consideration of Coulomb effect an enhancement of this ratio at low mt is found compatible with that observed in these experiments. Our calculations are based on previous (3+1) dimensional hydrodynamical simulations (HYLANDER), which described many other aspects of experimental data. In this model the observed enhancement is a consequence of baryon and strangeness conservation and of chemical equilibration of the system and is caused by the decay of produced hyperons, which leads to a difference in the total number of positive and negative pions as well. Based on the same approach, we also present results for the π/π ratio for S + S (CERN/SPS) collisions, where we find a similar effect. The absence of the enhancement of the π/π ratio in the S + S data presented by the NA44 Collaboration, if confirmed, could indicate that chemical equilibration has not yet been estabilished in this reaction. E. Mail: arbex@mailer.uni-marburg.de E. Mail: ornik@warp.soultek.de E. Mail: pluemer@mailer.uni-marburg.de E. Mail: schlei@t2.lanl.gov E. Mail: weiner@mailer.uni-marburg.de

Using a three-dimensional hydrodynamic simulation of the collision and an equation of state containing a first order phase transition to the quark-gluon plasma, we study thermal photon production for $Au+Au$ collisions at $E_{lab}=11.5$ AGeV and for $Pb+Pb$ collisions at $160$ AGeV. We obtain surprisingly high rates of thermal photons even at the lower energy, suggesting that, contrary to what was expected so far, photon production may be an interesting topic for experimental search also at the Alternating Gradient Synchrotron. When applied to the reaction $S+Au$ at $200$ AGeV, our model can reproduce preliminary data obtained by the WA80 Collaboration without having to postulate the existence of an extremely long-lived mixed phase as was recently proposed.